Using controlled rectifiers like this usually isn't regarded as a SMPS, though. (Notably because this technique does not allow to select the switching frequency

Using controlled rectifiers like this usually isn't regarded as a SMPS, though. (Notably because this technique does not allow to select the switching frequency, which is fixed by the grid in this circuit, so this circuit does not allow high-frequency switching, which is one of the main reasons SMPSs are much lighter than traditional power supplies -- the higher frequencies mean a much smaller core can be used while avoiding saturation). Using SCRs or triacs to pre-regulate the voltage of a linear regulator was a very common technique well into the late 80s for high power, precision power supplies. The power supply shown here works very much the same, except there being no linear post-regulation stage. Contrast this with the HV generation in devices using CRTs, which early on (~50s) started to use high-frequency converters, usually of the resonant kind.